Ignition system



3,312,211 IGNITHON SYSTEM Wesley D. Boyer, Franklin, Mich., assignor to The Ford Motor Company, Dearhorn, Mich., a corporation of Delaware Filed Oct. 13, 1964, Ser. No. 403,451 4 Claims. (Cl. 123148) -This invention relates to an ignition system for an internal combustion engine, and more particularly to an ignition system for a internal combustion engine in which a capacitive storage element is charged by a measured amount of electrical energy and is then discharged into the ignition coil at a given time during the ignition cycle.

This invention is a modification of the invention of applcation S.N. 403,263, filed Oct. 12, 1964, in the name of Ole K. Nilssen and assigned to the assignee of this invention. In that patent application there is described an ignition system in which a measured amount of electrical energy is delivered to a primary winding of an ignition coil by connecting the storage battery or source of electrical energy in the automotive vehicle to this primary winding for a short constant time period immediately prior to the requirement for ignition voltages. This is done by the use of a solid state switching device or transistor coupled to a saturable switching core that determines and controls the on time of the solid state switching device or transistor, and hence the energization of the primary Winding of the ignition coil. In that invention, the energy storage element is the primary winding of the ignition coil or inductor as is conventional in ignition systems.

In the present invention, the electrical storage element is a capacitor instead of an inductor, and this allows charging current to be drawn in measured amounts at any convenient time by retaining the charge on the capacitor until it is needed to fire the spark plugs of the engine. The capacitor permits efficient energy storage with precise timing of its release to provide proper ignition voltages.

In the invention, the saturable switching core and solid state switching device or transistor are employed to energize a primary winding of a transformer for a short constant time period. This energization commences when a set of breaker points operated in synchronism with the engine open or when some equivalent device reduces a bias applied to the saturable switching core and ends when the saturable switching core reaches saturation. When the time period for charging of this primary winding has elapsed and the solid state switching device is switched to a nonconduoting state by the saturable switching core, the energy is transferred through a secondary winding at stepped up voltages to a storage capacitor. This storage capacitor is coupled to the primary winding of an ignition coil through a solid state switching device, preferably in the form of a controlled rectifier. This solid state switching device or controlled rectifier prevents discharge of the capacitor through the primary winding until the solid state switching device or controlled rectifier is switched to a conducting state. A control winding is provided on the transformer to switch the solid state switching device or controlled rectifier into a conducting state when the breaker points or other equivalent device operated in synchronism with the engine operates to again charge the primary winding of this transformer through the first mentioned solid state switching device. The conduction of the second mentioned solid state switching device or controlled rectifier discharges the capacitor through the primary winding of the ignition coil and ignition voltages are generated in the secondary windmg.

In accordance with this invention then, a measured amount of electrical energy is stored in a capacitor I United States Patent through the operation of a solid state switching device and a saturable switching core that controls this device. When the next cycle of operation commences to again provide this measured amount of electrical energy, the capacitor is discharged under the control of another solid state switching device to provide proper ignition voltages. After the capacitor is discharged, a measured amount of electrical. energy is again stored therein for the next ignition cycle.

'Thus, the present invention provides a very efficient ignition system that charges the system with only the necessary amount of electrical energy to perform the ignition function at all engine operating speeds. provides for precise timing of the release of this energy to provide precise ignition timing. It has been found that this system can be operated at very high engine speeds Without any significant deterioration in ignition or engine performance.

An object of the present invention is the provision of an ignition system for an internal combustion engine that draws only a precise measured amount of electrical energy suflicient to perform the ignition function with this energy being discharged into the spark plugs of the engine in a precise timing relationship.

A further object of the invention is an ignition system for an internal combustion engine in which precise timing is achieved together with excellent high speed performance characteristics and lowenergy dissipation, particularly at low engine speeds and stalling conditions.

Other objects and attendant advantages of the present invention will be more readily realized when the specification is considered in connection with the attached drawing in which:

FIGURE 1 is an electrical circuitdiagram of the ignition system of the present invention, and

FIGURE 2 is a hysteresis curve of the saturable switching core used with the invention.

Referring now to the drawings in which like reference numerals designate like parts throughout the several views thereof, there is shown in FIGURE 1 a source of electrical energy in the form of an electrical storage battery 10 having a negative terminal 11 connected to a base lead or line 12 through a lead 13. The positive terminal 14 of the electrical storage battery 10 is connected throughlead 15 to junction 16. The junction 16 is in turn connected through lead 17 to one terminal of winding 18 positioned on saturable switching core 21. The other terminal of the winding 18, the dot marked terminal, is connected through lead 2-2 and resistor 23 to movable arm 24 of a set of ignition contact breaker points 25. 'This set of ignition contact breaker points 25 includes a first contact 26 positioned on and electrically connected to movable arm 24 and a second stationary contact 27 connected to lead 12 through lead 29. The movable arm 24 of the set of ignition contact breaker points 25 is periodically operated to periodicallyopen and close the contacts 26 and 27 by means ofa cam 31 and follower 32. The cam. 31 is operated in synchronism with the internal combustion engine.

The junction 16 connected to the positive terminal 14 of electrical storage battery 10 through lead 15 is also connected to the dot marked terminal of winding 35 of saturable switching core 21 through lead 36. The other terminal of winding 35 is connected through lead 37 to a junction 38, and the junction 38 is connected through lead 41 to an output electrode 42, in the form of an emitter,

of a solid state switching device or transistor 43. The

This tap 47 divides a winding 51 of transformer 48 into It also a primary winding 52 and a secondary winding 53. The primary winding is connected at the end opposite tap 47 to ground line or lead 12 through a lead 54.

The'junction 38 that is connected to the output electrode 42 or emitter of the solid state switching device or transistor 43 is also connected through lead 56 to the dot marked terminal of feedback winding 57 wound on saturable switching core 21. The other end of winding 57 is connected through lead 58 and resistor 61- to the control electrode or base 62 of the solid state switching device or transistor 43. A resistor 63 is also coupled between the lead 41 and the lead 58.

The end of the primary winding 52 of the transformer 48 connected to lead 54 is connected through this lead, lead 12 and lead 71 to one plate 72 of a capacitor 73. The other plate 74 of this capacitor is connected through lead 75 to a junction 76. This junction is connected to the anode 77 of a diode 78, and the cathode 81 of the diode 78 is connected to the dot marked terminal of the secondary winding 53 of transformer 48 through a lead 82.

The plate 72 of the capacitor 73 is also connected through the lead 71, the lead 12 and a lead 84, to the dot marked terminal of the primary winding 85 of ignition coil 86. The tap 87 of the ignition coil 86 is connected to the anode 88 of a solid state switching device, preferably in the form of a controlled rectifier 91 through a lead 92. The cathode 93 of the solid state switching device or controlled rectifier 91 is connected to junction 76 through a lead 94.

The control electrode 96 of the controlled rectifier 91 is connected through lead 97, lead 98, and resistor 99 to the dot marked terminal of control winding 101 of the transformer 48. The other end of the control winding 101 is connected back to junction 76 through a lead 77. The control electrode 96 and the cathode 93 of the controlled rectifier 91 are coupled through lead 97, resistor 103,and the lead 94. The junction 76 and hence plate 74 of capacitor 73 is connected to a resistor 104 through lead 105. The resistor is in turn connected to the anode 106 of diode 107. The cathode 108 of diode -7 is connected through lead 109 to junction 45 and collector 44 of solid state switching device or transistor 43.

The secondary winding 110 of the ignition coil 86 is connected through lead 111 to rotating arm 112 of distributor 113. This rotating arm 112 sequentially couples the secondary winding 110 of ignition coil 86 to spark plugs 114 through leads 115 through 120.

In the operation of the ignition system shown in FIG- URE 1, with the ignition contact breaker points 25 closed, a circuit from the storage battery 10 will be established through the winding 18 of saturable core 21. The ampere turns present as a result of this circuit biases the saturable switching core 21 into its negative state of saturation (minus B max.), as shown in FIGURE 2. The legend N I of FIGURE 2 represents the ampere turns of magnetizing force impressed upon the saturable core 21 due to current flow through winding 18. The transistor or solid state switching device 43 at this time is in its nonconducting state because of the low resistance represented by resistors 61 and 63 positioned between the control electrode or base 6 2 and the output electrode or emitter 42.

When the contact breaker points 25 open, a transient voltage is induced in winding 57 of a polarity to turn this transistor or solid state switching device 43 to a conducting state. This polarity relationship can be readily realized by an examination of the dot marked terminals of windings 18 and 57. A positive transient voltage will appear at the dot marked terminal with respect to the unmarked terminal of winding 18 when the contact breaker points 25 open and the solid state switching core falls from B max. to the remnant flux density indicated by the letter B-. This action will induce a transient voltage in winding 57 as previously described, with a plus voltage at the dot marked terminal with respect to the voltage at the unmarked terminal.

Turning on of the solid state switching device or transistor 43 permits current flow through it and through the winding 35 on the saturable switching core 21. This current flow is of a polarity to switch the saturable switching core into its saturated condition represented by +B max. This can. be seen readily by reference to the dot marked terminals since current into or a positive voltage at the dot marked terminal will provide ampere turns to drive the core towards +B max. The ampere turns of magnetizing force created by this current through the Winding 35 is indicated by the legend N I in FIGURE 2.

During the time that the saturable switching core 21 is being switched to the saturable condition at +13 max., the voltage will be maintained across the feedback winding 57 thereby driving the transistor or solid state switching device 43 into a full state of saturation. Current then fiows through the primary winding 52 of transformer 48 via this solid state switching device or transistor 43. As soon as the saturable switching core 21 saturates, the feedback voltage in the winding 57 disappears and the transistor commences to turn off. The decreased current through the winding 35 permits the core to fall back toward its remnant flux density thereby generating a reverse bias voltage in the feedback winding 57. This rapidly brings the transistor or solid state switching de vice 43 toa nonconducting state thereby de-energizing the primary winding 52 of transformer 48.

The on time of the transistor or solid state switch 43 is determined by the time it takes to switch the saturable switching core 21 from its negative to its positive state of saturation. The resistor 63 limits and lengthens the reverse voltage developed in the feedback winding 57 thereby helping to prevent the solid state switching device of transistor 43 from turning back on. The resistor 61 determines to a large extent the duration of the on time since it helps to determine the actual voltage across he feedback winding 57, and may be adjusted to yield the desired initial energy charge to the primary winding 52 of the transformer 48. Also, this resistor 61 may be "shorted out during cranking to provide a convenient means of compensating for the reduced input voltage and consequently lower energy storage during engine cranking operations.

As the transistor or solid state switching device 43 is turned off, the collapsing magnetic field in the primary winding 52 of transformer 48 induces a high voltage in the secondary winding 53, since transformer 48 is a stepup transformer. The voltage of the secondary winding 53 is added to the self-induced voltage generated in the primary winding 52, and the energy in the two windings 52 and 53 charges energy storage capacitor 73 through the diode 78. The capacitor charging current can be shown to have a waveform which is a quarter cycle of cosine function. The voltage on the capacitor 73 is sustained at the peak of this Waveform because the diode 78 becomes reverse biased at this time and the solid state switch or controlled rectifier 91 is in a nonconducting "state. As can be appreciated by an examination of the dot marked terminals of transformer 48, the control winding 101 has a voltage induce-d therein at this time of a polarity to keep the solid state switching device or controlled rectifier 91 biased to a nonconducting state.

After the energy has been stored in the capacitor 73, the ignition contact breaker points 25 will close thereby re-establi'shing electrical energy in the winding 18 of the saturable switching core 21 and again switching the core into the -B max. saturated condition. This action induces a reverse bias in the feedback winding 57 to keep the solid state switching device or transistor 43 in its non conducting state.

When the ignition contact breaker points 25 again open to initiate another cycle of charging of the primary winding 52 of the transformer 48 by turning on the solid state Switching device or transistor 43, a positive pulse of electrical energy will be generated at the dot marked terminal of the control winding 101 since the voltage across winding 52 will be positive at its dot marked terminal. This is of a proper polarity to turn the solid state switching device or controlled rectifier 91 into a conducting state, and the capacitor 73 at this time discharges through the primary winding 85 of the ignition coil 86, and the solid state switching device or controlled rectifier 91. This generates a high voltage in the secondary Winding 101 of the ignition coil 86 that is applied to one of the spark plugs 114 through lead 111, rotating arm 112 and one of the leads 115 through 120. After the discharge ofthe capacitor 73, the controlled rectifier 91 will be turned oif, and another cycle will commence.

The circuit of the diode 107 and resistor 104 connected between the junction 76 and the junction 75 has several purposes. The leakage reactance components in the transformer 51 due to the imperfect coupling of the windings 52, 53 and 101, may cause troublesome spikes of voltage immediately following the turn-off of the transistor or solid state switching device 43. The diode 107 forms a connection between the Winding 52, the capacitor 73, and the collect-or 44 of the solid state switching device or transistor 43. Thus, when the spikes of voltage due to the leakage reactance occur, a path is provided through the capacitor 73 and the diode 107 so that the amplitude of these spikes is limited, and this limits the reverse voltage that would otherwise be applied across the solid state switching device or transistor 43. This energy, or at least a good portion of it, is stored on the capacitor 73. The energy in this leakage reactance spike may be as great as 20% of the total energy in the transformer 51, and the recovery and transfer of a portion of this energy to the capacitor 73 increases the over-all efficiency of the ignition system.

As pointed out, the capacitor 73 is discharged through the primary winding 85 of ignition coil 86 by the conduction of the controlled rectifier 91 when the transistor or solid state switching device 43 is brought to its conducting state and energency fiows through the primary winding 52 of transformer 51. When the discharge of the capacitor 73 occurs, the diode 107 clamps the capacitor to a reverse voltage approximately equal to the voltage of the source of electrical energy since the voltage at junction 45 will be approximately equal or slightly less than the terminal voltage of the source of electrical energy 10 when the transistor or solid state switching device 43 is conducting. It has been found that this limiting of the reverse voltage on the capacitor 73 to a value close to the terminal voltage of the source of electrical energy 10 has the effect of lengthening the duration of the discharge of the arc through the spark plugs 114 to approximately double the duration without the diode 107 in the circuit. This has a very desirable effect under certain conditions, particularly under light load-lean mixture conditions, since proper combustion may not occur with short time duration arcs under this condition.

Thus, the present invention provides a means for metering a given amount of electrical energy to the ignition system, and for delivering it to the spark plugs of the engine in precise timed relationship. It also permits the system to be installed in an automotive vehicle without altering of the advance mechanism of a conventional distributor used in a standard ignition system.

As indicated on the drawing of FIGURE 1, the rotating arm 112 of the distributor 113 is operated in synchronism with cam 31 so that the ignition contact breaker points 25 open when the rotating arm is connected to one of the leads 115 through 120. Since the capacitor 73 is discharged upon the opening of the ignition contact breaker points 25, it can be appreciated that this system can be readily employed with a conventional distributor mechanism with no alternation in the timing mechanism of the distributor.

It is to be understood that this invention is not to be limited to the exact construction shown and described, but that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

I claim:

1. An ignition system for an internal combustion engine comprising, a source of electrical energy, an ignition coil including a primary and a secondary winding, a plurality of spark plugs, means operable in synchronism with the engine for sequentally coupling said secondary winding of said ignition coil with said spark plugs, a set of breaker points operable in synchronism with the engine and opening when said means couples said secondary winding of said ignition coil to each of said spark plugs, a step up transformer including a primary winding, a secondary winding and a control winding, means coupled to said source of electrical energy, said primary winding of said transformer and said set of breaker points for coupling said source of electrical energy to said primary winding of said transformer for a predetermined constant time irrespective of the speed of the engine when said breaker points open and while the breaker points remain open, a capacitor coupled to said secondary winding of said transformer receiving the electrical energy from said transformer after said predetermined constant time has elapsed, a solid state switching device having a pair of output electrodes and a control electrode, said primary winding of said ignition coil, said output electrodes of said solid state switching device and said capacitor coupled in series, said control electrode coupled to said control winding of said step up transformer, said control winding being wound to apply a pulse of electrical energy to said control electrode of a polarity to cause said solid state switching device to conduct when said breaker points open thereby discharging the electrical energy stored in said capacitor through said primary winding of said ignition coilv when said breaker points open.

2. An ignition system for an internal combustion engine comprising, a source of electrical energy, an ignition coil including a primary and a secondary winding, a plurality of spark plugs, means operable in synchronism with the engine for sequentially coupling said secondary winding of said ignition coil with said spark plugs, ignition actuating means operable in synchronism with the engine and actuated when said means couples said secondary winding of said ignition coil to each of said spark plugs, a step up transformer including a primary winding, a secondary winding and a control winding, means coupled to said source of electrical energy, said primary winding of said transformer and said ignition actuating means for coupling said source of electrical energy to said primary winding of said transformer for a predetermined constant time irrespective of the speed of the engine when said ignition actuating means is actuated, said source of electrical energy being uncoupled from said primary winding prior to the next actuation of the ignition actuating means, a capacitor coupled to said secondary winding of said transformer receiving the electrical energy from said transformer after said predetermined constant time has elapsed, a solid state switching device having a pair of output electrodes and a control electrode, said output electrodes of said solid state switching device coupled to said capacitor and said primary winding of said ignition coil for permitting discharge of said capacitor through said primary winding of said ignition coil when said solid state switching device is in a conducting state and for preventing discharge of said capacitor through said primary winding of said ignition coil when said solid state switching device is in a non-conducting state, said control electrode coupled to said control winding of said step up transformer, said control winding being wound to apply a pulse of electrical energy to said control electrode of a polarity to cause said solid state switching device to conduct when said ignition actuating means is actuated thereby discharging the electrical energy stored in said capacitor through said primary winding of said ignition coil when said ignition means is actuated.

3. An ignition system for an internal combustion engine comprising, a source of electrical energy, an ignition coil including a primary and a secondary winding, a plurality of spark plugs, means operable in synchronism with the engine for sequentially coupling said secondary winding of said ignition coil with said spark plugs, a set of breaker points operable in synchronism with the engine and opening when said means couples said secondary winding of said ignition coil to each of said spark plugs, a capacitor coupled to said primary Winding of said ignition coil, a

transformer having a primary winding, a secondary winding and a control winding, circuit means producing current in the transformer primary winding when the breaker points open and stopping the current a predetermined time thereafter While the breaker points are still open, said secondary winding charging said capacitor when current through the primary winding stops, and circuit means coupled to said control winding for discharging said capacitor through the ignition coil primary winding on the next successive opening of said set of breaker points.

4. An ignition system for an internal combustion engine comprising a source of electrical energy, an ignition coil including a primary and a secondary winding, a plurality of spark plugs, means operable in synchronism with the engine for sequentially coupling said secondary winding of said ignition coil with said spark plugs, ignition actuating means operable in synchronism with the engine and actuated when said means couples said secondary winding of said ignition coil to each of said spark plugs, a capacitor coupled to said primary winding of said ignition coil, a transformer having a primary winding, a secondary Winding and a control winding, circuit means permitting current from said source of electrical energy in the transformer primary winding when the ignition actuating means is actuated and stopping the current a predetermined time thereafter while the breaker points are still open, said secondary winding charging said capacitor when current through the transformer primary winding stops, and circuit means coupled to said control winding for discharging said capacitor through the ignition coil primary winding on the next successive actuation of said ignition actuating means.

References Cited by the Examiner UNITED STATES PATENTS 2,899,632 8/1959 Lawson 123148 X 3,150,285 9/1964 Mieras. 3,150,286 9/1964 Quinn 123-148 X 3,263,124 7/ 1966 Stuermer.

MARK NEWMAN, Primary Examiner. LAURENCE M. GOODRIDGE, Examiner. 

1. AN IGNITION SYSTEM FOR AN INTERNAL COMBUSTION ENGINE COMPRISING, A SOURCE OF ELECTRICAL ENERGY, AN IGNITION COIL INCLUDING A PRIMARY AND A SECONDARY WINDING, A PLURALITY OF SPARK PLUGS, MEANS OPERABLE IN SYNCHRONISM WITH THE ENGINE FOR SEQUENTALLY COUPLING SAID SECONDARY WINDING OF SAID IGNITION COIL WITH SAID SPARK PLUGS, A SET OF BREAKER POINTS OPERABLE IN SYNCHRONISM WITH THE ENGINE AND OPENING WHEN SAID MEANS COUPLES SAID SECONDARY WINDING OF SAID IGNITION COIL TO EACH OF SAID SPARK PLUGS, A STEP UP TRANSFORMER INCLUDING A PRIMARY WINDING, A SECONDARY WINDING AND A CONTROL WINDING, MEANS COUPLED TO SAID SOURCE OF ELECTRICAL ENERGY, SAID PRIMARY WINDING OF SAID TRANSFORMER AND SAID SET OF BREAKER POINTS FOR COUPLING SAID SOURCE OF ELECTRICAL ENERGY TO SAID PRIMARY WINDING OF SAID TRANSFORMER FOR A PREDETERMINED CONSTANT TIME IRRESPECTIVE OF THE SPEED OF THE ENGINE WHEN SAID BREAKER POINTS OPEN AND WHILE THE BREAKER POINTS REMAIN OPEN, A CAPACITOR COUPLED TO SAID SECONDARY WINDING OF SAID TRANSFORMER RECEIVING THE ELECTRICAL ENERGY FROM SAID TRANSFORMER AFTER SAID PREDETERMINED CONSTANT TIME HAS ELAPSED, A SOLID STATE SWITCHING DEVICE HAVING A PAIR OF OUTPUT ELECTRODES AND A CONTROL ELECTRODE, SAID PRIMARY WINDING OF SAID IGNITION COIL, SAID OUTPUT ELECTRODES OF SAID SOLID STATE SWITCHING DEVICE AND SAID CAPACITOR COUPLED IN SERIES, SAID CONTROL ELECTRODE COUPLED TO SAID CONTROL WINDING OF SAID STEP UP TRANSFORMER, SAID CONTROL WINDING BEING WOULD TO APPLY A PULSE OF ELECTRICAL ENERGY TO SAID CONTROL ELECTRODE OF A POLARITY TO CAUSE SAID SOLID STATE SWITCHING DEVICE TO CONDUCT WHEN SAID BREAKER POINTS OPEN THEREBY DISCHARGING THE ELECTRICAL ENERGY STORED IN SAID CAPACITOR THROUGH SAID PRIMARY WINDING OF SAID IGNITION COIL WHEN SAID BREAKER POINTS OPEN. 